1. Field of the Invention
This invention relates to a method for producing organo metal chlorides directly from a molten metal. More particularly, this invention relates to a method for producing organo indium chlorides by contacting an organo chloride with an indium metal melt to form an organo indium chloride. The direct contact of the organo chloride with the indium metal melt results in the production of either diorgano indium chloride or organo indium dichloride depending on the contacting time and efficiency of the process. Additionally, activator compounds are optionally added to the metal melt to enhance the reaction rate. Gallium metal is also suitable for use with the inventive method for forming organo gallium chlorides.
2. Summary of Related Art
Organo metal chlorides are organo-metallic compounds that dissociate under pyrolytic reaction conditions. The dissociation permits the use of the compounds as a source for metal in chemical vapor deposition processes. Thus, the organo metal chlorides, particularly organo indium chlorides, are desirable for use as precursors in chemical vapor deposition processes for laying down metal oxide or doped metal oxide films or coatings onto substrates. Additionally, the deposition rates of indium oxide, or doped indium oxides, through the use of organo indium chlorides as precursors, are higher than other conventional indium precursors. The higher deposition rates are desirable for applying coatings on substrates, such as a continuous glass ribbon in a float glass production process. Higher deposition rates result in thicker coatings on the substrate which correspond to improved energy attenuation properties for the coated article.
Conventional methods of producing organo indium chlorides generally involve either ligand exchange or alkylation of an indium compound to form the desired organo indium halide. The noted techniques require the use of solvents or pyrophoric compounds which result in additional processing or separation steps to obtain the desired organo indium chloride. Additionally, the known techniques for producing organo indium chlorides possess relatively long reaction times. Gmelin Handbook of Inorganic and Organometallic Chemistry: In, Organoindium Compounds 1, 8th Edition; Wolfgang Petz, Ed.; Springer-Verlag, Berlin: 1991.
Organo indium chlorides are produced through alkylation of indium trichloride with an alkyl lithium compound. This is typically the most used procedure for generating organo indium chlorides. The reaction is generally carried out in a solvent of diethyl ether, benzene, or toluene for about 1 to 2 days under agitation. Upon completion of the reaction, the desired organo indium chloride is separated through sublimation.
An additional method of producing organo indium chlorides involves ligand exchange between indium trichloride and trialkyl indium, a pyrophoric compound. The reaction is carried out in ether, benzene, or toluene and provides quantitative yields in less than 6 hours.
Additionally, Comprehensive Organometallic Chemistry, eds. Geoffrey Wilkinson; F. Gordon A. Stone; Edward W. Abel, Pergamon Press, Oxford, 1982, vol. I, chp.7. discloses that indium metal, in general, reacts slowly with alkyl bromides or iodides. The reaction rate is enhanced when activated indium metal is utilized. The activation of the metal is accomplished by reacting indium trichloride with potassium in solution. The mixture is refluxed under nitrogen for four to six hours yielding a finely divided black metal powder. The powder reacts with the noted alkyl halide to form dialkyl indium bromide or iodide.
Thus, known methods of producing organo indium chlorides require alkylation or ligand exchange processes. The reactions are typically carried out in a solvent and therefore, require additional processing or separation steps to recover the desired organo indium chloride. The conventional methods also require extended reaction times. Activators may also be added to the indium metal to enhance the reaction process with halides. However, conventional indium activators involve compounds that result in additional processing steps to enhance the recovery of the desired organo metal halide.
It would be an advantage to produce an organo indium chloride directly from indium metal using an organo chloride as the organo group Source. The direct synthesis of an organo indium chloride from indium metal would eliminate the use of pyrophoric compounds or the production of organo indium chlorides in a form that does not require additional solvents, processing, or separation techniques. Furthermore, it would be advantageous to develop a method with significantly reduced reaction times over those required with conventional organo indium chloride processes. The direct synthesis of organo indium chlorides from an indium metal melt would therefore improve the economics of producing the compounds over known processes.
It would also be advantageous to utilize an activator in the indium metal melt during the direct synthesis of organo indium chlorides. An activator would accelerate the reaction rate of the organo indium chloride from the indium melt.
It would be a further advantage to utilize an activator that would regenerate within the indium metal melt once the generation of organo indium chloride is initiated. The regeneration of an activator enhances the continuation of the reaction with the addition of fresh reactants, but without adding additional activators.